The present invention relates to containers and, in particular, to containers for the storage and/or transport of nuclear fuel elements.
Typically, nuclear fuel elements may be stored and/or transported in containers in the form of casks, racks for in-pond storage of spent nuclear fuel elements, flasks and multi-element bottles. These containers generally comprise an elongate body incorporating a plurality of compartments of rectangular cross section, each of which can accommodate a fuel element. The compartments are formed from elongate plates, which intersect one another at right angles to define a cellular grid structure.
A problem encountered in the construction of such containers concerns the joining together of the plates along their longitudinal edges. One method of joining the plates is to weld the plates together. However, this method has certain disadvantages. For example, the plates are usually made from materials such as stainless steel or boron steel which are extremely difficult to weld. Furthermore, the welding material used to form fillet welds occupies space within the compartments so that the passage of a fuel element along a compartment may be obstructed. A further disadvantage is that plates joined together by welds are prone to distortion due to the intense heat generated during the welding process. A combination of interlinked plates of different sets secured against disassembly by welding is disclosed in EP-A-0 883 135 (A.T.E.A.).
It is an object of this invention to provide a container for nuclear fuel elements in which the plates forming the compartments are joined together in such a manner as to overcome the aforementioned disadvantages.
According to the present invention there is provided a container for the storage and transport of nuclear fuel elements comprises a plurality of elongate compartments for receiving the nuclear fuel elements, the compartments being defined by a first set of plates intersecting with a second set of plates, the first set of plates extending perpendicularly with respect to the second of plates to define compartments having a rectangular cross section, characterised in that the plates include an interlocking joint, the interlocking joint comprising at least one projection provided on one plate of one set and a recess formed in the other plate of the same set, and wherein a retaining portion is provided in the recess for engagement by the projection so as to interlock the plates.
Preferably, the plates in the first set are interconnected by an interlocking joint comprising a plurality of projections spaced along a longitudinal edge of one of the plates and a plurality of recesses spaced along a longitudinal edge of the other plate.
The projection may comprise a first portion extending forwardly from the longitudinal edge of the said one of the plates and an arm portion extending laterally from an end of the first portion, and wherein the arm portion engages with the retaining portion in the recess.
Preferably, an arm portion extends from each side of the first portion, the recess having two retaining portions, each of which is engaged by an arm portion.
The first portion and each arm portion may define a substantially T-shaped projection and wherein the recess is correspondingly T-shaped.
Each arm portion may be formed by a deflectable tab extending rearwardly and outwardly from an end of the first portion, the tabs being deflected inwardly as the projection is pushed into the recess, the tabs tending to resume their undeflected positions when the projection is located in the recess. Suitably, the recess has a first passage region extending into an enlarged region, the junction of the first passage region and the enlarged region defining the retaining means.
At an intersection of the first and second set of plates the recess may be provided in a plate of the second set.
Suitably, at an intersection of the first and second set of plates at least one tenon projects from each of the mutually facing longitudinal edges of the plates of the second set, the tenons extending into a slot provided in the plate of the first set.
The tenons projecting from each of the mutually facing longitudinal edges of the plates of the second set are preferably received by the same slot.
Preferably, the tenons on each of the longitudinal edges are provided with interengaging latch portions.
The profiles of the projections and recesses forming the interlocking joints can be formed by any suitable metal cutting operation. However, it has been found that the most suitable method is a laser cutting technique. This technique enables the interlocking joints to be produced with the required dimensional accuracy.
It has been found that the interlocking joints according to the invention provides the container the ability to withstand static and dynamic loads. The resilience of the joints enables the container to absorb energy resulting from impacts.
Construction of the container in accordance with the present invention enables the components to be transported conveniently as so-called xe2x80x9cflat packsxe2x80x9d. Container assembly can be carried on site by unskilled labour.
The absence of weld material within the compartments ensures that there is an increased amount of space for accommodating the fuel elements. Furthermore, there are no obstructions within the compartments to hinder insertion of the fuel elements. Since no heat is required for assembly the plates, in contrast to a welded assembly, the plates are not prone to distortion.
The plate defining the compartments may have a thickness in the order of 5 mm. If the containers are required to accommodate spent nuclear fuel elements, the material for the plates should be a suitable neutron poison. Typically, the material may be a stainless steel or a boron steel.